The present invention relates to centrifugal pumps and more particularly to the volute casing for such a pump. In a volute casing, flow area increases as one proceeds from the cutwater of the pump to the exit throat. The volute configuration causes the pump to be more efficient since it keeps the stream flow constant. If a volute configuration were not employed, one would have turbulence.
A significant problem encountered with such pumps is that a radial load is imposed on the impeller shaft, particularly when the pump is operating either below or above its best-efficiency-point capacity. Such radial loading creates problems of wear, leakage at the seal(s), the need for larger bearings and stiffer impeller shafts.
One way in which radial thrust can be reduced, at least to some extent, is through the use of a dual volute or double volute casing in which an internal wall known as a splitter extends around the impeller for 180.degree., dividing the annular chamber surrounding the impeller into two volute chambers. Such a splitter generally starts at a point approximately 180.degree. opposite the cutwater. I have also heretofore suggested the production of volute casings employing a fake tongue or splitter located generally opposite the cutwater and extending for only a short distance, rather than the full 180.degree. of a normal splitter.
However, such casings are more expensive to cast particularly where the splitter is a full 180.degree. partition. Also, casings are heavier and more difficult to clean. Consequently, this construction is usually provided only in larger size pumps.
As a result, there has long been a need for alternative means for reducing the radial load or thrust on an impeller shaft so as to minimize wear, leakage, the need for larger bearings and stiffer shafts.